It is already known that a cyanine dye of which the side chain of a mother nucleus (a heterocyclic ring directly bonded to a polymethine chain) is a sulfoalkyl group is used for a photographic material. The sulfoalkyl group is generally bonded to the quaternary nitrogen of a nitrogen-containing heterocyclic ring which constitutes the mother nucleus of the cyanine dye.
The above cyanine dye having the sulfoalkyl group directly bonded to the quaternary nitrogen is generally produced from a precursor, i.e., an alkyl sulfonate derivative having a heterocyclic ring, which has the following formula (5) or (7): ##STR2## wherein X represents --O--, --S--, --NR.sup.1 --, --Se--, --Te-- or --CR.sup.2 R.sup.3 -- (in which each of R.sup.1, R.sup.2 and R.sup.3 independently represents a hydrogen atom or a lower alkyl group which may have a substituent and R.sup.2 and R.sup.3 may form a ring by bonding each other), Y represents a hydrogen atom, mercapto group, an alkylthio group which may have a substituent and an alkyl group, n represents an integer of 0 to 6, and R represents a substituent, the substituents being the same or different from each other in the case of n of not less than 2. The cyanine dye obtained by the compound represented by the formula (5) or (7) is described in Japanese Patent Provisional Publications No. 1-187543 and No. 3-105339.
For example, an alkyl sulfonate derivative containing a nitrogen-atom can be prepared by causing a nitrogen containing compound (e.g., amine) to react with a chain alkyl sulfonate (salt) activated by introducing a halogen atom or sulfonyloxy group to bond the sulfoalkyl group to the nitrogen.
This method is considered to be applied to the preparation of the alkyl sulfonate derivative having a nitrogen-containing heterocyclic ring represented by the above formula (5) or (7). In more detail, it would be considered that a nitrogen-containing heterocyclic compound having the following formula (4) or (6): ##STR3## wherein Y, X, R, n and Z represent the meanings defined above; is caused to react with a chain alkyl sulfonate (salt) activated above to bond the sulfoalkyl group to the nitrogen, whereby the alkyl sulfonate derivative presented by the above formula (5) or (7) is obtained.
The activated alkyl sulfonate serves advantageously as a sulfoalkylated agent for a compound to be sulfoalkylated, in the case that the compound has a high nucleophilicity so that its sulfoalkylated reaction proceeds under relatively mild conditions. However, in the case that the nitrogen-containing heterocyclic compound of the above formula (4), which has not a benzene ring but a naphthalene ring, is caused to react with the activated chain alkyl sulfonate (salt), the reaction needs more heating due to its low reactivity so that the activated portion of the alkyl sulfonate is apt to eliminate. Hence, the alkyl sulfonate derivative represented by the above formula (5) can not be obtained using the alkylsulfonate.
Otherwise, as an sulfoalkylated agent having an activated hydrogen, an aliphatic sultone is already known. It is described in Japanese Patent Provisional Publication No. 1-187543 that the aliphatic sultone reacts with a nitrogen-containing heterocyclic compound such as a compound having the above formula (6) to introduce a sulfoalkyl group into the heterocyclic compound, whereby the alkyl sulfonate derivative of the above formula (5) is obtained. Generally, introduction of the sulfoalkyl group into the nitrogen-containing heterocyclic compound of the above formula (4) having a naphthalene ring is also conducted in the same manner as above. Thus, in the case that the sultone is caused to react with the nitrogen-containing heterocyclic compound of the above formula (4) or (6) to bond the nitrogen of the heterocyclic compound, the alkyl sulfonate derivative of the above formula (5) or (7) would be obtained. Because the elimination occurring in use of the activated chain alkyl sulfonate hardly occurs in the case of use of the sultone.
However, the study of the present inventor has revealed that the reaction of the sultone with the nitrogen-containing heterocyclic compound of the above formula (4) gives the derivative in an extremely low yield. The reason is deemed as follows:
A steric hindrance derived from a hydrogen atom or substituent which is bonded to 8.position carbon atom (on naphthalene ring) of the nitrogen-containing heterocyclic compound of the above formula (4), inhibits the sultone molecule from approach to the nitrogen atom of the nitrogen-containing heterocyclic compound.